The present invention relates to a mold clamping mechanism that clamps a pair of molds under high pressure in molding of resin and an injection molding machine using the mold clamping mechanism.
The injection molding machine has a mechanism (a mold clamping mechanism) that clamps metal molds continuously from when injection of molten resin is started to when the resin completely solidifies in order to prevent the metal molds from being separated from each other by the pressure produced through the injection of the molten resin.
As the mold clamping mechanism, for example, a type shown in FIG. 14 is known. Specifically, a mold clamping mechanism 71 has a fixed die plate 72 and a rear plate 73, which are connected together by a plurality of tie bars (shafts) 74. A movable die plate 75 is arranged between the fixed die plate 72 and the rear plate 73. Each of the tie bars 74 is passed through the movable die plate 75. A first metal mold 76 is attached to the fixed die plate 72, and a second metal mold 77 is attached to the movable die plate 75. A ball screw 78 extends through the rear plate 73 with an end (the left end as viewed in FIG. 14) of the ball screw 78 fixed to the movable die plate 75. A nut 79 is rotatably provided in the rear plate 73 and the ball screw 78 is threaded to the nut 79. A motor 80, which drives and rotates the nut 79, is fixed to the rear plate 73. Thus, when the motor 80 of the mold clamping mechanism 71 operates the nut 79 to rotate, the ball screw 78 axially moves relative to the rear plate 73. This axially moves the movable die plate 75, which is fixed to the ball screw 78, with the tie bars 74 guiding the movable die plate 75. In this manner, the second metal mold 77, which is attached to the movable die plate 75, selectively approaches and separates from the first metal mold 76. In molding of resin, the second metal mold 77 is brought into contact with the first metal mold 76 and then pressed against the first metal mold 76 through further movement of the ball screw 78.
Another type of mold clamping mechanism is described in Japanese Laid-Open Patent Publication No. 5-269748. Specifically, as shown in FIG. 15, a mold clamping mechanism 81 has a fixed die plate 83 to which a first metal mold 82 is attached. A ball screw 84 is rotatably supported by each of the four corners of the fixed die plate 83 through a bearing 85. A second metal mold 86 is attached to a movable die plate 87. A ball nut 88 is provided at each of the four corners of the movable die plate 87. The ball screws 84 are each threaded to the corresponding one of the ball nuts 88. A motor 90 is connected to the fixed die plate 83 through a bracket 89. The ball screws 84 are operably connected to an output shaft 91 of the motor 90 through couplings 92. Thus, when the motor 90 of the mold clamping mechanism 81 operates the ball screws 84 to rotate, the movable die plate 87 moves in the axial direction of the ball screws 84. This causes the second metal mold 86 to selectively approach and separate from the first metal mold 82, together with the movable die plate 87. In molding of resin, the second metal mold 86 is brought into contact with the first metal mold 82 and then pressed against the first metal mold 82 through further rotation of the ball screws 84.
[Patent Document 1] Japanese Laid-Open Patent Publication No. 5-269748
However, in order to press the second metal mold 77 against the first metal mold 76, the mold clamping mechanism 71 employs the fixed die plate 72, the movable die plate 75, and the tie bars 74, additionally to the first and second metal molds 76, 77. The first metal mold 76 is attached to the fixed die plate 72 and the second metal mold 77 is attached to the movable die plate 75. The positions of the ball screw 78 and the nut 79 are changed relative to each other to move the movable die plate 75 in such a manner that the second metal mold 77 is pressed against the first metal mold 76. In other words, the mold clamping mechanism 71 uses various components other than the direct targets of pressing, which are the first and second metal molds 76, 77, and thus becomes large-sized. Also, since the movable die plate 75, which is heavy, is moved to move the second metal mold 77, the motor 80 must be a large-sized type with great output torque. This further enlarges the size of the mold clamping mechanism 71.
Also, although the mold clamping mechanism 81 of Japanese Laid-Open Patent Publication No. 5-269748 does not include any tie bar, the mold clamping mechanism 81 employs the fixed die plate 83 and the movable die plate 87 additionally to the first metal mold 82 and the second metal mold 86. Accordingly, like the above-described case, the mold clamping mechanism 81 becomes disadvantageously large-sized.